It is proposed to study the arterial baroreceptor reflex control of arterial pressure in chronically instrumented dogs both under conscious condition and under anesthesia. An identical perturbation should be used in both circumstances so that the arterial pressure response to the perturbation can be compared between the two conditions. The same responses are to be determined before and after denervation of the major arterial baroreceptor afferent nerves, i.e., carotid sinus and vagal nerves in order to determine the open-loop gain of the reflex. The perturbations usable in conscious dogs are (1) elevation or lowering of the dog's head (on its own) by a high equivalent to 20 mmHg, and (2) a quick hemorrhage from the artery by 10% of its blood volume, and restitution after 10 min of observation. For the spontaneous head-level change, the dog is trained for weeks to put his head into either one of the two boxes which are lit alternatingly every two minutes. For the hemorrhage experiments, the dog is trained to lie quietly on its side. Besides arterial pressure, aortic flow, heart rate and total peripheral resistance are also determined. BIBLIOGRAPHIC REFERENCES: Kostiuk, D.P., K. Sagawa, A.A. Shoukas: Modification of the flow-generating capability of the canine heart-lung compartment by the carotid sinus baroreceptor reflex. Circ. Res. 38: 546-553, 1976. Suga, H., K. Sagawa, D. P. Kostiuk: Controls of ventricular contractility assessed by pressure-volume ratio, Emax. Cardiovas. Res. 10: 582-592, 1976.